1. Field of the Invention
The present invention relates to fireplaces, and, more particularly, to direct vent wood burning fireplaces.
2. Description of the Related Art
Direct vent fireplaces are typically used for gas fireplace applications. A combustion air duct provides combustion air from an outside ambient environment to the combustion chamber at a location which is at or below the base of the fire within the combustion chamber. When the gas burner is ignited a natural draft is created within the flue pipe which causes a low pressure area below the fire and pulls the combustion air through the combustion air duct into the combustion chamber. An access door disposed in one wall of the combustion chamber may be sealed with the framework of the fireplace to ensure that an adequate siphon affect occurs within the combustion chamber to draw the combustion air through the combustion air duct and into the combustion chamber.
Gas fireplaces have a relatively low heat input and volumetric flow rate of combustion products when compared to a conventional wood burning fireplace. For example, a conventional gas fireplace has a predetermined supply of gas (such as by a fixed orifice) which is fed to the burner and may be selectively turned on or off. The predetermined supply of gas has an energy input of between 20,000-40,000 BTU/hour, which in turn results in an operating temperature at the inlet to the flue of about 600.degree. F., and does not exceed 1000.degree. F. for conventional units. A fire in a gas fireplace having an energy input level of only 20,000-40,000 BTU/hour in turn results in a lesser demand for combustion air into the combustion chamber. As a result, a direct vented gas fireplace may receive all of the required combustion air through the combustion air duct.
Solid fuel, e.g., wood, burning fireplaces may include a combustion air duct which provides combustion air from the outside ambient environment to the interior of the combustion chamber. However, with conventional units, the combustion air duct does not supply all of the combustion air required for proper combustion within the fireplace. To wit, in contrast with a gas fireplace which may typically have an energy input of, e.g., 20,000-40,000 BTU/hour, a wood burning fireplace has an energy input which begins near zero and may approach 250,000 BTU/hour during operation, or even greater. Such an energy input in turn requires a much larger supply of combustion air into the combustion chamber for proper combustion. Wood burning fireplaces having a combustion air duct do not receive a sufficient amount of combustion air through the combustion air duct for proper combustion. Rather, combustion air is utilized from both the outside ambient environment and the room in which the fireplace is located.
Wood burning fireplaces of conventional design may include a glass door at the front of the fireplace, but the door is not sealed with the combustion chamber and a portion of the combustion air used within the combustion chamber is drawn into the combustion chamber from the room in which the fireplace is located. In fact, glass access doors for a wood burning fireplace are purposefully designed to effect a flow of combustion air into the combustion chamber from the room in which the fireplace is located. Wood burning fireplaces therefore use a substantial amount of combustion air from the room in which the fireplace is located, with attendant disadvantages associated therewith, e.g., negative pressure and indoor air quality problems.
More specifically, newer homes in which a fireplace is located are built fairly air-tight to conserve energy costs associated with heating and cooling. However, products placed within the house such as a water heater or furnace may utilize some of the air within the house as combustion air. This may cause a negative ambient pressure within the home, relative to the outside ambient environment. A wood burning fireplace which uses combustion air from the room in which the fireplace is located also contributes to the negative pressure problem within the house. A negative pressure within the house will cause cold air from the outside ambient environment to flow into the house through various openings, e.g., bathroom vents, chimneys, etc., resulting in a loss of overall energy efficiency.
Further, in contrast with a gas fireplace which is instantaneously turned off by stopping the flow of gas to the burner, a wood burning fireplace has a burn-down period in which the fire continues to smolder within the combustion chamber. When the fire is smoldering, the heat output of the fire is relatively small and there is only a small natural draft which occurs through the flue pipe. Because of negative pressure which may exist within the house, combustion products may flow from the combustion chamber past the non-sealed door and into the room in which the fireplace is located. That is, the lower pressure within the room in which the fireplace is located (relative to the interior of the combustion chamber or to the outside atmosphere), may cause combustion products produced by the smoldering fire to flow into the room. Discharge of such combustion products into the house is obviously not desirable.
What is needed in the art is a wood burning fireplace which provides all of the necessary combustion air to the combustion chamber from the outside ambient environment, and does not utilize combustion air from the room in which the fireplace is located.
A further need is a wood burning fireplace which supplies all of the combustion air from the outside ambient environment without utilizing combustion air from the room in which a fireplace is located, while at the same time providing sufficient combustion air to the combustion chamber for a solid fuel energy input of greater than 75,000 BTU/hour.
A further need is a direct vent wood burning fireplace which may introduce the combustion air at the top of the combustion chamber (e.g., above the base of the fire), and does not require the use of ducting, plenums, etc. having a long flow path for introducing the combustion air at the bottom of the combustion chamber in one of the side walls or the bottom wall.